Motor drive with silicon carbide MOSFET switches

ABSTRACT

Motor drive power conversion systems are provided including a rectifier and a switching inverter, wherein the switching devices of the rectifier, the inverter and/or of a DC/DC converter are silicon carbide switches, such as silicon carbide MOSFETs. Driver circuits are provided for providing bipolar gate drive signals to the silicon carbide MOSFETs, including providing negative gate-source voltage for controlling the off state of enhancement mode low side drivers and positive gate-source voltage for controlling the off state of enhancement mode high side drivers.

REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/698,925, filed Apr. 29, 2015, entitled MOTOR DRIVE WITH SILICONCARBIDE MOSFET SWITCHES, which claims priority to and the benefit of,U.S. Provisional Patent Application No. 61/988,744, filed May 5, 2014,and entitled MOTOR DRIVE WITH SILICON CARBIDE MOSFET SWITCHES, theentirety of which applications are hereby incorporated by reference.

BACKGROUND INFORMATION

The subject matter disclosed herein relates to power conversion systems.

BRIEF DESCRIPTION

One or more aspects of the present disclosure are now summarized tofacilitate a basic understanding of the disclosure, wherein this summaryis not an extensive overview of the disclosure, and is intended neitherto identify certain elements of the disclosure, nor to delineate thescope thereof. Rather, the primary purpose of this summary is to presentvarious concepts of the disclosure in a simplified form prior to themore detailed description that is presented hereinafter. The presentdisclosure provides power conversion systems for driving a motor orother AC load with silicon carbide switches.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram;

FIG. 2 is a schematic diagram;

FIG. 3 is a schematic diagram;

FIG. 4 is a schematic diagram;

FIG. 5 is a schematic diagram;

FIG. 6 is a schematic diagram;

FIG. 7 is a schematic diagram;

FIG. 8 is a schematic diagram;

FIG. 9 is a schematic diagram; and

FIG. 10 is a schematic diagram.

DETAILED DESCRIPTION

Referring initially to FIGS. 1 and 2, FIG. 1 illustrates an exemplarymotor drive power conversion system 10 receiving single or multiphase ACinput power from an external power source 2. The illustrated examplereceives a three phase input, but other multiphase embodiments arepossible. The motor drive 10 includes an input filter circuit 20, inthis case a three phase LCL filter having grid side inductors L1, L2 andL3 connected to the power leads of the power source 2 as well as seriesconnected converter side inductors L4, L5 and L6, with filter capacitorsC1, C2 and C3 connected between the corresponding grid and converterside inductors and a common connection node, which may but need not beconnected to a system ground. Although illustrated in the context of athree phase LCL filter circuit 20, other alternate circuitconfigurations can be used, including without limitation LC filters.Moreover, although illustrated as including an input filter circuit 20,the filter circuit 20 may be omitted or modified in other embodiments.The motor drive 10 includes a rectifier 30, a DC bus or DC link circuit40 and an output inverter 50, with the rectifier 30 and the inverter 50being operated by a controller 60. The controller 60 includes arectifier controller 62 and an inverter controller 66 respectivelyproviding rectifier and inverter switching control signal 62 a and 66 ato the rectifier 30 and the inverter 50 to operate switches thereof. Incertain implementations, the inverter switching controller 66 providesthe control signal 66 a in order to selectively operate the individualinverter switching devices S7-S12 to provide a variable frequency,variable amplitude output to drive the motor load 4, and the inverterswitching controller 66 also provides a setpoint or desired DC signal orvalue to the rectifier switching controller 62. The rectifier switchingcontroller 62, in turn, operates the rectifier switching devices S1-S6in order to provide a regulated DC voltage Vdc across a DC linkcapacitor C4 in the intermediate link circuit 40 according to thedesired or setpoint DC signal or value.

The controller 60 and the components thereof may be implemented as anysuitable hardware, processor-executed software, processor-executedfirmware, logic, and/or combinations thereof wherein the illustratedcontroller 60 can be implemented largely in processor-executed softwareor firmware providing various control functions by which the controller60 receives feedback and/or input signals and/or values (e.g.,setpoint(s)) and provides rectifier and inverter switching controlsignals 62 a and 66 a to operate the rectifier switching devices S1-S6and switches S7-S12 of the inverter 50 to convert input power forproviding AC output power to drive the load 4. In addition, thecontroller 60 and the components thereof can be implemented in a singleprocessor-based device, such as a microprocessor, microcontroller, FPGA,etc., or one or more of these can be separately implemented in unitaryor distributed fashion by two or more processor devices. Moreover, theswitching controllers 62 and 66 may provide any suitable form of switchcontrol, including one or more forms of pulse width modulation (PWM)control in providing the switching control signals 62 a and/or 66 a andvarious embodiments. Furthermore, the switching control components 62and 66 may include suitable driver circuitry for providing gate controlsignals to operate silicon carbide switching devices S1-S12.

FIG. 2 illustrates another embodiment of a variable frequency, variableamplitude motor drive power conversion system 10, in this case a currentsource converter including a current source rectifier 30 with siliconcarbide switching devices S1-S6 and a current source inverter 50 withsilicon carbide switching devices S7-S12, where the converter stages 30and 50 are coupled with one another via an intermediate DC link circuit40 including one or more DC link chokes or inductors L. In this case,the rectifier switching controller 62 operates the rectifier switchingdevices S1-S6 in order to provide a regulated DC link current in theintermediate circuit 40, and the current source inverter 50 providesvariable frequency, variable amplitude output currents to drive themotor load 4.

The illustrated motor drives 10 in FIGS. 1 and 2 implement an activefront end (AFE) including a switching rectifier (also referred to as aconverter) 30 receiving three-phase power from the source 2 through thefilter circuit 20. The rectifier 30 includes silicon carbide MOSFETrectifier switches S1-S6 operable according to a corresponding rectifierswitching control (e.g., gate) signals 62 a to selectively conductcurrent when actuated. In addition, as seen in FIGS. 1 and 2, diodes areconnected across the individual silicon carbide switches S1-S6, althoughnot a strict requirement of all embodiments. Operation of the rectifierswitches S1-S6 is controlled according to pulse width modulatedrectifier switching control signals 62 a in certain embodiments toprovide active rectification of the AC input power from the source 2 toprovide a DC bus voltage Vdc across a DC bus capacitance C4 in a DC linkcircuit 40 (FIG. 1) and/or to provide a DC link current in theintermediate circuit 40 (FIG. 2). The rectifier 30, moreover, may becontrolled in a regeneration mode, with the switching devices S1-S6operative according to corresponding switching control signal 62 a fromthe controller 62 to regenerate power from the intermediate circuit 40through the filter 20 (if included) and back to the source 2. Moreover,the front end rectifier 30 may be controlled in order to implement otherfunctions in the motor drive 10, including without limitation powerfactor correction, selective harmonic elimination, etc. In variousembodiments, moreover, the active rectifier 30 may be replaced with apassive rectifier, with a switching inverter 50 including a plurality ofsilicon carbide switching devices S7-S12. Moreover, an active rectifier30 may be operated at or near a line frequency of the AC input source(fundamental front end or FFE operation) or at a higher and possiblyvariable switching frequency, such as an active front end (AFE)rectifier.

The inverter switches S7-S12 in this embodiment are also silicon carbideMOSFET devices coupled to receive power from the DC bus 40 and toprovide AC output power to the motor or other load 4. Moreover, whilethe illustrated inverter 50 is a three-phase stage, other single ormultiphase inverters 50 may be provided in various embodiments. Thesilicon carbide MOSFET switches S7-S12 are operated according to gatecontrol switching control signals 66 a from the inverter switchingcontrol component 66, and can be any form of silicon carbide MOSFETs orother silicon carbide-based semiconductor switching devices. Thecontroller 60 in certain embodiments receives various input signals orvalues, including setpoint signals or values for desired outputoperation, such as motor speed, position, torque, etc., as well asfeedback signals or values representing operational values of variousportions of the motor drive 10.

Silicon carbide (SiC), also known as carborundum, is a compoundincluding silicon and carbon and can be any suitable stoichiometry toimplement a semiconductor switching device S1-S12. Silicon carbideswitching devices S1-S12, moreover, are preferably high temperature/highvoltage devices, suitable for use in various motor drives 10. Forexample, the switches S1-S12 are each rated at 1200 V and 300 A incertain embodiments, as shown in the attached appendix, and the drive 10in the non-limiting embodiment of FIG. 1 is a low-voltage variablefrequency drive with a rating from about 50 W through about 1 kW todrive motor loads from about 0.25 hp through 30 hp at voltages in therange of about 100-600 V. The medium voltage current source converterembodiment 10 of FIG. 2 has a power range of about 200-3400 hp andsupply voltages of about 2400-6600V AC. In certain embodiments, thesilicon carbide switching devices S1-S12 preferably have fairly largecontinuous current ratings, for example, at 25° C. and/or any higherrated temperature seen in a closed control cabinet or other motor driveenclosure (not shown), and have controllable threshold voltages over atemperature range of about 25° C. through about 200° C., and low RDSONover such normal operating temperature ranges. In addition, theswitching devices S1-S12 preferably have high switching energy ratings.

The silicon carbide switching devices S1-S6 of the active front endrectifiers 30, and the silicon carbide inverter switches S7-S12,moreover, can be any suitable form of field effect transistor, such asan enhancement mode or depletion mode MOSFET in various embodiments. Inthe non-limiting examples of FIGS. 1 and 2, the switching devices areenhancement mode MOSFETs, with the controller 60 providing suitablecontrol signals (e.g., Vgs) accordingly. Other embodiments are possible,for example, in which all the switching devices S1-S6 and S7-S12 of agiven one of the conversion stages 30, 50 can be either enhancement modeor depletion mode FETs. FIGS. 3 and 4 illustrate further exemplaryembodiments, and which two or more of the switching devices S1-S12 canbe provided in a single module or package. For instance, FIG. 3illustrates an enhancement mode N-channel silicon carbide MOSFETembodiment including six switching devices S which can be interconnectedfor providing a silicon carbide switching rectifier 30 and/or switchinginverter 50. In this case, terminals are provided for the source anddrain terminals of the included switches S, as well as for the controlgates thereof. FIG. 4 illustrates another possible implementation,including a set of three half-bridge silicon carbide MOSFET modules, inthis case N-channel devices S, where each module includes two siliconcarbide switches S. The switching devices S and/or modules containingmultiple such switching devices S, moreover, may be physically packagedand/or structure to provide drop-in replacement for IGBTs or otherconventional motor drive switching devices in certain embodiments,thereby allowing or facilitating upgrading of existing drives.

The inventors have appreciated that silicon carbide switching devicesmay advantageously provide benefits compared with IGBTs and othersilicon-based switches in motor drive applications, whether for activerectification in the rectifier stage 30, an intermediate DC/DC converterfeeding the inverter 50, an auxiliary power supply DC/DC converterand/or in driving the motor load using a switching inverter 50. Forinstance, silicon carbide switching devices S1-S12 provide improved(e.g. higher) bandgap energy, and better (e.g., higher) thermalconductivity compared with silicon IGBTs. Moreover, the wide bandgapsilicon carbide switching devices S1-S12 may provide higher breakdownelectric field, and are capable of higher blocking voltages, higherswitching frequencies, and higher junction temperatures than silicondevices.

Referring now to FIGS. 5 and 6, FIG. 5 illustrates a power conversionsystem embodiment including DC/DC converter stages 42 within each of aplurality of motor drive 10 for providing DC input power to theassociated inverters 50. The DC/DC converters 42 in this example arepowered from a shared DC bus via first and second DC bus connections DC+and DC−. The DC/DC converters 42 can be used for a variety of purposes,including without limitation providing individualized DC inputs to theassociated inverters 50. The input rectifier 30 can be a passiverectifier in certain embodiments, or the input rectifier 30 can be anactive front end switching rectifier for performing power factorcorrection and other functions in the shared DC bus system. FIG. 6 showsanother system configuration with a single rectifier 30 providing a DCoutput shared among a plurality of inverters 50, including a drive 10having an inverter 50 and an auxiliary DC/DC converter supply 42receiving input power from the shared DC bus via lines DC+ and DC−. Inthis example, the inverters 50 each receive DC input power at the sameDC voltage level, as does the DC/DC converter 42. The disclosed conceptscan be employed in any type or form of DC/DC converter, wherein theillustrated flyback converters 42 are merely a non-limiting example.

The inventors have appreciated that noise or voltage fluctuations on theshared DC bus lines may result from switching operation of the variousconnected drives inverters 50 and any other loads such as the DC/DCconverter 42 in FIG. 6. In accordance with the present disclosure, theinverters 50, the DC/DC converters 42 and/or a switching input rectifier30 include one or more silicon carbide switching devices, for example,silicon carbide MOSFETs. In the inverters 50 and/or a switching inputrectifier 30, moreover, the silicon carbide switches may be operativelycoupled with an associated one of the first and second DC bus lines DC+and DC−, respectively. The inventors have further appreciated thatfluctuations or noise on an associated DC bus line DC+ or DC− can affectswitching operation of the host converter stage 30, 42 and/or 50. Inthis regard, the threshold voltage VT associated with silicon carbideMOSFET devices generally decreases with increasing operatingtemperature, and the inventors have appreciated that use of siliconcarbide MOSFET switches in one or more of the converter stages 30, 42and/or 50 in the presence of fluctuations along the DC+ and/or DC− buslines may inhibit the ability to reliably ensure the off-state usingconventional gate driver circuitry.

Referring also to FIG. 7, further aspects of the present disclosureprovide driver circuitry 70 for providing switching control signalswhich can be used with enhancement mode devices and/or with depletionmode silicon carbide switches in first and second states respectivelyabove and below the associated DC bus connection. In the example of FIG.7, the DC/DC converter 42 is a single switch flyback converter which canbe used as an auxiliary power supply for providing control power forcircuitry of a motor drive power conversion system 10. In otherexamples, the flyback DC/DC converter 42 can be used as an intermediateconverter receiving DC input power from a shared rectifier 30 andproviding a DC output for use by an associated switching inverter 50(e.g., FIG. 5 above). The DC/DC converter 42 in FIG. 7 provides anoutput voltage VO and receives DC input power from the first and secondDC bus connections DC+ and DC−. The converter 42 includes a siliconcarbide converter switching device 46 operative to provide a DC outputvia a flyback transformer T1 according to a converter switching controlsignal 41 received from a driver circuit 70. The driver circuit 70 inthis example provides the converter switching control signal 41 to thegate G of the silicon carbide MOSFET device 46 in a first state at afirst voltage above the voltage of the associated DC bus connection DC−in order to turn the N-channel device 46 on, thereby allowing current toflow from the DC+ bus connection through a primary winding PR of thetransformer T1 to the lower DC bus connection DC−. A primary windingreset circuit 44 is connected in parallel with the primary winding PR,and includes a series connection of a first diode D1 and first resistorR1, with a capacitor C5 connected in parallel with the resistor R1 asshown. The driver circuit 70 also provides the converter switchingcontrol signal 41 in a second state at a second voltage below thevoltage of the DC− bus connection in order to turn the silicon carbideMOSFET device 46 off. The alternating on and off states of the siliconcarbide MOSFET switch 46 provide alternating current in first and secondsecondary windings SC1 and SC2, respectively, of the transformer T1. Inthis example, the secondary winding SC1 provides alternating current toa rectifier diode D2 and a filter capacitor C6 is connected from thecathode of D2 to the lower winding connection of the secondary windingSC1 to provide a DC output voltage VO for use in powering one or morecontrol circuits of a motor drive conversion system 10 and/or for use asan input to a switching inverter 50 (e.g., FIG. 5 above).

The illustrated silicon carbide switching device 46 is an N-channelenhancement mode MOSFET having a gate terminal G, a drain terminal D anda source terminal S as shown in FIG. 7. In addition, the silicon carbideMOSFET 46 has a nominally positive threshold voltage VT, which decreaseswith increasing switch operating temperature. The inventors haveappreciated that provision of a negative off-state gate-source voltageVGS by the driver circuit 70 provides additional assurance that theswitch 46 will be reliably in the off state even in the presence ofshifting voltages along the corresponding DC bus connection DC−, andeven at elevated operating temperatures with corresponding reduced(e.g., positive) MOSFET threshold voltage levels. In the embodiment ofFIG. 7, the driver circuit 70 includes a driver supply circuit formed bythe secondary winding SC2, a rectifier diode D3 and a filter capacitorC7 to provide a DC voltage between a first voltage node VCC and a secondvoltage node VEE of the driver circuit 70. The driver supply circuitryfurther includes a Zener diode Z1 with an anode connected to anintermediate node, and a capacitor C8 connected between the intermediatenode and the second voltage node VEE. In addition, the intermediate nodeis connected to the lower DC bus connection DC−.

In operation of one non-limiting example, the driver supply circuitincluding the secondary winding SC2, the diode D3 and the capacitor C7provides a voltage of approximately 25 V DC between VCC and VEE, and theZener diode Z1 has a Zener voltage of approximately 20 V. In thisregard, the output voltage of the driver supply circuit can be tailoredby adjustment of the turns ratio between the primary winding PR and thesecondary winding SC2 of the transformer T1, with the positive andnegative voltage levels at the voltage nodes VCC and VEE relative to theintermediate node being set by the Zener voltage of Z1. Moreover, theintermediate node of the branch circuit formed by Z1 and C8 is connectedto the lower DC bus connection DC−. Thus, in steady state operation, thevoltage (relative to DC−) of the first voltage node VCC is approximately20 V according to the Zener voltage of Z1, and the voltage at VEE isapproximately −5 V DC. In addition, a resistance R3 is connected fromthe first DC bus connection DC+ to initially provide voltage to the VCCnode, where the resistance R3 can be a string of multiple resistors incertain embodiments.

The driver circuit 70 in the example of FIG. 7 includes a driver stage49 with a PMOS transistor MP1 and an NMOS transistor MN1 receiving acontrol signal from a pulse width modulation (PWM) controller 48 andproviding a switching control signal output 41 through a resistance R2to the gate G of the switching device 46. In this example, the PWMcontroller 48 provides a pulse width modulated output based on asetpoint input SP and on a current feedback signal 47 (IFB) representingthe switching current flowing through the silicon carbide MOSFET switch46 and a voltage feedback signal 45 (VFB) from an isolation circuit 43representing the DC/DC converter output voltage VO. In a first statewith the PWM controller output low, MP1 is on and the N-channel siliconcarbide enhancement mode MOSFET 46 is on. In a second state with the PWMcontroller output high, MP1 is off and MN1 is on and the switchingcontrol signal 41 is pulled negative relative to the source voltage(DC1) to ensure that the switch 46 is off.

The illustrated DC/DC converter 42 of FIG. 7 advantageously employs asingle silicon carbide MOSFET switch 46, and may be used in one examplefor the DC bus of a 690 VAC drive with a blocking voltage rating for theswitch 46 of 1700 V and current rating above 4 A. Unlike typical siliconMOSFET devices of similar current rating having a maximum voltage ratingof only 1500 V, the illustrated design is a single switch flybackconfiguration. Use of conventional silicon MOSFET switching devices forDC bus applications of a 690 VAC drive would require the use of twoMOSFET switches to accommodate the high DC bus voltage. Thus, the use ofsilicon carbide switching devices in an auxiliary power supply or otherflyback DC/DC converter advantageously reduces the number of switchingdevices, thereby saving cost and space.

FIG. 8 shows another conversion system configuration with a rectifier 30(active or passive) and an output bus capacitance C4 providing a DC busvoltage Vdc on bus connection lines DC+ and DC−, and a switchinginverter 50 including silicon carbide MOSFET switching devices S7-S12including enhancement type high side switches S7-S9 with sourceterminals coupled with DC+ and enhancement type low side switchesS10-S12 with source terminals coupled with DC−. The high side switchesS7-S9 are controlled by inverter switching control signals from a highside driver circuit 66H based on signaling from an inverter pulse widthmodulation (PWM) circuit 691. In this case, the high side switchingcontrol signals 66 a are provided at first states at or near acorresponding positive voltage VCCH for turning on the MOSFET and secondstates at or near a voltage VEEH for turning off the MOSFET, where eachupper or high side switch is driven by a corresponding driver in thecircuit 66H and each individual high side driver is provided with acorresponding set of supply lines VCCH and VEEH referenced to therespective silicon carbide MOSFET source. The low side silicon carbideswitches S10-S12 are provided with switching control signals 66 a from alow side driver circuit 66L according to signaling from the PWM circuit691 at first and second states at corresponding voltages VCCL and VEEL,where VCCL is a positive voltage for turning on the MOSFET and VEEL is anegative voltage for turning off the MOSFET. In one example as shown inFIG. 8, the low side switches are driven using a common set of supplylines VCCL and VEEL. In another example, the low side switches areindividually driven using a corresponding set of supply lines VCCL andVEEL.

As seen in FIG. 8, the driver circuit 70 also includes driver supplycircuits generating the voltages VCCH, VEEH, VCCL and VEEL. In thisexample, a transformer T1 includes a primary winding PR connected inseries with a switch 74 between DC+ and DC−, with the switch 74 beingoperated by a timer circuit 72 in order to selectively conduct currentthrough the primary winding PR to generate current flow in first andsecond secondary windings SCH and SCL. This example include three highside supply secondaries SCH and associated rectifier supply circuits D4and C9 with a zener ZH and capacitor C10 individually referenced to therespective silicon carbide MOSFET source of the associated high sideinverter switch S7-S9. The secondary windings SCH and SCL are coupledwith rectifier diodes D4 and D5 and output capacitors C9 and C 11 toprovide the voltages at the nodes VCCH, VEEH, VCCL and VEEL, forexample, 25 V DC for supplying the high and low side driver circuits 66Hand 66L, respectively. The individual high side driver supply circuitsin this example each include a Zener diode ZH coupled between VCCH and afirst intermediate node coupled with the MOSFET source terminal, alongwith a capacitor C10 coupled between the MOSFET source terminal andVEEH. For a Zener voltage of approximately 20 V, and a transformer turnsratio providing 25 V DC between VCCH and VEEH, the high side drivervoltage VCCH in a first state is approximately 20 V above the MOSFETsource terminal node to ensure turn on of the high side switches S7-S9and the voltage VEEH is approximately 5 volts below the MOSFET sourceterminal node to turn off the high side silicon carbide switches. Inthis manner, the driver circuit 70 provides adequate gate voltageheadroom to ensure complete turnoff of each of the enhancement modesilicon carbide MOSFET high side switching devices S7-S9, even in thepresence of noise on the DC bus and/or high operating temperature andthe corresponding reduced silicon carbide MOSFET threshold voltagelevels.

As further shown in FIG. 8, the low side driver supply circuitryprovided by the secondary winding SCL, rectifier diode D5, capacitorsC11 and C12, and a low side supply Zener ZL is set in one example withappropriate turns ratio to provide approximately 25 V DC between VCCLand VEEL, with the intermediate node joining ZL and C12 being coupledwith the MOSFET source terminal, which is the same as the second DC busconnection DC−, thereby operating in conjunction with the low sidedriver circuit 66L to provide low side switching control signals at VCCLof approximately 20 V above the voltage of DC− and VEEL approximately 5V below the voltage of DC−. Driven at these voltage levels, the siliconcarbide MOSFET low side switching devices S10-S12 are ensured to beproperly turned on and off even at high operating voltages andtemperatures in the presence of noise or other voltage transients on theDC− bus connection.

It is noted in the example of FIG. 8 that the driver supply voltagesVCCH, VEEH, VCCL and VEEL are provided generally independent of theoperation of the inverter 50 as these are derived from the DC busvoltage Vdc. Thus, establishment of the DC bus voltage prior tooperation of the inverter 50 ensures that the driver supply voltagesVCCH, VEEH, VCCL and VEEL are at the desired levels by operation of thetimer circuit 72 and the switch 74 prior to use in generating theinverter switching control signals 66 a.

FIG. 9 illustrates use of similar driver circuitry 70 for providingswitching control signals to silicon carbide high side active rectifierswitching devices S1-S3 at first and second states with voltagesrespectively above and below the voltage of the first DC bus connectionDC+ via high side driver circuitry 62H provided with supply voltagesVCCH and VEEH from a setoff three high side driver supply circuits (onlyone illustrated in FIG. 9) individually including a secondary windingSCH, a diode D4, a Zener ZH and capacitors C9 and C 10 generally asdescribed above in connection with FIG. 8. In addition, the low siderectifier switching devices S4-S6 (N-channel silicon carbide MOSFETswitches) are driven by low side driver circuitry 62L to provideswitching control signals 62 a at first and second levels VCCL and VEELrespectively above and below the voltage of DC− via supply circuitrySCL, D5, ZL, C11 and C12. The primary winding PR of the transformer T1in this embodiment is connected between the DC bus lines DC+ and DC− andis driven generally as described above in connection with FIG. 8 toprovide the advantageous silicon carbide MOSFET switching device driversignal levels via the driver circuit 70 using the driver DC supplyvoltages between VCCH and VEEH and between VCCL and VEEL independent ofactual switching operation of the active rectifier 30.

FIG. 10 illustrates another non-limiting example in which an activerectifier 30 and a switching inverter 50 include silicon carbide MOSFETswitching devices, where the high side rectifier switching devices arecontrolled using switching control signal 62 a from high side drivercircuitry 62H (e.g., as described above in connection with FIG. 9) atswitch-specific voltage levels VCCH and VEEH according to signals from arectifier PWM circuit 69R, and the low side rectifier switching devicesare driven by signals 62 a at levels VCCL and VEEL from low side drivercircuitry 62L based on signals from the PWM circuit 69R. Also in thisexample, the switching inverter 50 includes silicon carbide high sidedevices driven using signals 66 a from a high side driver circuit 66H atswitch-specific levels VCCH and VEEH, and the silicon carbide low sideinverter switches are driven at levels VCCL and VEEL by low side drivercircuitry 66L (e.g., as described above in connection with FIG. 8). Thedriver circuitry 70 includes separate driver supply circuits for therectifier 30 and the inverter 50, each creating the driver voltagesVCCH, VEEH, VCCL and VEEL via a transformer primary winding PR connectedto the DC bus lines DC+ and DC− generally as described above inconnection with FIG. 8. In this configuration, the controlled drivervoltage levels are provided independent of operation of the switchingdevices of the rectifier 30 and of the switching devices of the inverter50, and can accommodate operation at elevated temperatures (e.g.,lowered silicon carbide MOSFET threshold voltages) and/or noise or othervoltage deviations in the DC bus voltage Vdc. In this manner, variousbenefits of the use of silicon carbide switching devices and motordrives and other power conversion systems are facilitated.

The above examples are merely illustrative of several possibleembodiments of various aspects of the present disclosure, whereinequivalent alterations and/or modifications will occur to others skilledin the art upon reading and understanding this specification and theannexed drawings. In particular regard to the various functionsperformed by the above described components (assemblies, devices,systems, circuits, and the like), the terms (including a reference to a“means”) used to describe such components are intended to correspond,unless otherwise indicated, to any component, such as hardware,processor-executed software, or combinations thereof, which performs thespecified function of the described component (i.e., that isfunctionally equivalent), even though not structurally equivalent to thedisclosed structure which performs the function in the illustratedimplementations of the disclosure. In addition, although a particularfeature of the disclosure may have been disclosed with respect to onlyone of several implementations, such feature may be combined with one ormore other features of the other implementations as may be desired andadvantageous for any given or particular application. Also, to theextent that the terms “including”, “includes”, “having”, “has”, “with”,or variants thereof are used in the detailed description and/or in theclaims, such terms are intended to be inclusive in a manner similar tothe term “comprising”.

The following is claimed:
 1. A power conversion system, comprising: anactive rectifier comprising a plurality of silicon carbide rectifierswitching devices coupled to receive AC input power from an externalpower source, and operative to provide a DC output signal according to aplurality of rectifier switching control signals, the active rectifierincluding a plurality of low side silicon carbide switches operativelycoupled with a DC bus connection; a switching inverter to convert the DCoutput signal to provide an AC output to drive a load; a controlleroperative to generate the rectifier switching control signals to operatethe rectifier switching devices; and a driver circuit operative toprovide a set of the switching control signals to the low side siliconcarbide switches in a first state at a first voltage above a voltage ofthe DC bus connection and in a second state at a second voltage belowthe voltage of the DC bus connection; and a driver supply circuit,including: a first voltage node providing a first supply voltage to thedriver circuit for providing the set of the switching control signals inthe first state at the first voltage above the voltage of the DC busconnection, a second voltage node providing a second supply voltage tothe driver circuit for providing the second set of the switching controlsignals in the second state at the second voltage below the voltage ofthe DC bus connection, an intermediate node connected to the DC busconnection, a zener diode with an anode connected to the intermediatenode and a cathode connected to the first voltage node to provide apositive voltage at the first voltage node with respect to theintermediate node, a capacitor connected between the intermediate nodeand the second voltage node to provide a negative voltage at the secondvoltage node with respect to the intermediate node, and a DC supplyproviding a positive DC voltage between the first and second voltagenodes.
 2. The power conversion system of claim 1, wherein the low sidesilicon carbide switches are enhancement mode devices.
 3. The powerconversion system of claim 1, wherein the low side silicon carbideswitches are depletion mode devices.
 4. The power conversion system ofclaim 1, wherein the power conversion system is a voltage sourceconverter motor drive.
 5. The power conversion system of claim 1,wherein the power conversion system is a current source converter motordrive.
 6. The power conversion system of claim 1, wherein the low sidesilicon carbide switches are P-channel silicon carbide MOSFETs.
 7. Thepower conversion system of claim 1, wherein the low side silicon carbideswitches are N-channel silicon carbide MOSFETs.
 8. The power conversionsystem of claim 1: wherein the rectifier includes: a plurality of highside silicon carbide switches operatively coupled with a first DC busconnection, wherein the plurality of low side silicon carbide switchesare operatively coupled with a second DC bus connection; and wherein thedriver circuit is operative to: provide a second set of switchingcontrol signals to the high side silicon carbide switches in a firststate at a third voltage above a voltage of the first DC bus connectionand in a second state at a fourth voltage below the voltage of the firstDC bus connection.
 9. The power conversion system of claim 8, whereinthe driver supply circuit includes: a second driver supply circuit,including: a third voltage node providing a third supply voltage to thedriver circuit for providing the second set of the switching controlsignals in the first state at the third voltage above the voltage of thefirst DC bus connection, a fourth voltage node providing a fourth supplyvoltage to the driver circuit for providing the second set of theswitching control signals in the second state at the fourth voltagebelow the voltage of the first DC bus connection, a second intermediatenode, a second zener diode with an anode connected to the secondintermediate node and a cathode connected to the third voltage node toprovide a positive voltage at the third voltage node with respect to thesecond intermediate node, a second capacitor connected between thesecond intermediate node and the fourth voltage node to provide anegative voltage at the fourth voltage node with respect to the secondintermediate node, and a second DC supply providing a positive DCvoltage between the third and fourth voltage nodes.
 10. The powerconversion system of claim 9, wherein the first DC supply includes afirst transformer secondary winding and a rectifier; and wherein thesecond DC supply includes a second transformer secondary winding and asecond rectifier.
 11. The power conversion system of claim 8, whereinthe low side silicon carbide switches are enhancement mode devices. 12.The power conversion system of claim 8, wherein the low side siliconcarbide switches are depletion mode devices.
 13. The power conversionsystem of claim 11, comprising: a driver supply circuit, including: afirst voltage node providing a first supply voltage to the drivercircuit for providing the set of the switching control signals in thefirst state at the first voltage above the voltage of the DC busconnection, a second voltage node providing a second supply voltage tothe driver circuit for providing the second set of the switching controlsignals in the second state at the second voltage below the voltage ofthe DC bus connection, an intermediate node connected to the DC busconnection, a zener diode with an anode connected to the intermediatenode and a cathode connected to the first voltage node to provide apositive voltage at the first voltage node with respect to theintermediate node, a capacitance connected between the intermediate nodeand the second voltage node to provide a negative voltage at the secondvoltage node with respect to the intermediate node, and a DC supplyproviding a positive DC voltage between the first and second voltagenodes.
 14. The power conversion system of claim 13, wherein the DCsupply includes a transformer secondary winding and a rectifier.
 15. Apower conversion system, comprising: an inverter comprising a pluralityof inverter switching devices coupled to receive DC input power andoperative to provide an AC output to drive a load according to aplurality of inverter switching control signals; a DC/DC converterreceiving DC input power and comprising at least one silicon carbideconverter switching devices operatively coupled with a DC bus connectionto provide a DC output signal to the inverter according to at least oneconverter switching control signal; a driver circuit operative toprovide the at least one converter switching control signal to the atleast one silicon carbide converter switching device in a first state ata first voltage above a voltage of the DC bus connection and in a secondstate at a second voltage below the voltage of the DC bus connection;and a driver supply circuit, including: a first voltage node providing afirst supply voltage to the driver circuit for providing the set of theswitching control signals in the first state at the first voltage abovethe voltage of the DC bus connection, a second voltage node providing asecond supply voltage to the driver circuit for providing the second setof the switching control signals in the second state at the secondvoltage below the voltage of the DC bus connection, an intermediate nodeconnected to the DC bus connection, a zener diode with an anodeconnected to the intermediate node and a cathode connected to the firstvoltage node to provide a positive voltage at the first voltage nodewith respect to the intermediate node, a capacitor connected between theintermediate node and the second voltage node to provide a negativevoltage at the second voltage node with respect to the intermediatenode, and a DC supply providing a positive DC voltage between the firstand second voltage nodes.
 16. The power conversion system of claim 15,wherein the DC supply includes a transformer secondary winding and arectifier.
 17. The power conversion system of claim 15, wherein theDC/DC converter provides control power for circuitry of the system. 18.The power conversion system of claim 15, wherein the at least onesilicon carbide converter switching device is an enhancement modesilicon carbide MOSFET.
 19. The power conversion system of claim 15,wherein the DC/DC converter is a flyback converter including atransformer primary winding coupled between a first DC bus connectionand the at least one silicon carbide converter switching device, the atleast one silicon carbide converter switching device being coupledbetween the transformer primary winding and a second DC bus connectionto control current flow in the transformer primary winding, and whereinthe driver circuit is operative to provide the at least one converterswitching control signal to the at least one silicon carbide converterswitching device in the first state at a first voltage above a voltageof the second DC bus connection and in a second state at a secondvoltage below the voltage of the second DC bus connection.
 20. The powerconversion system of claim 19, comprising: a driver supply circuit,including: a first voltage node providing a first supply voltage to thedriver circuit for providing the set of the switching control signals inthe first state at the first voltage above the voltage of the DC busconnection, a second voltage node providing a second supply voltage tothe driver circuit for providing the second set of the switching controlsignals in the second state at the second voltage below the voltage ofthe DC bus connection, an intermediate node connected to the DC busconnection, a zener diode with an anode connected to the intermediatenode and a cathode connected to the first voltage node to provide apositive voltage at the first voltage node with respect to theintermediate node, a capacitor connected between the intermediate nodeand the second voltage node to provide a negative voltage at the secondvoltage node with respect to the intermediate node, and a transformersecondary winding and a rectifier providing a positive DC voltagebetween the first and second voltage nodes.